Process for obtaining different gradations in developing silver halide emulsion layers



Patented Apr. 24, 1934 PROCESS FOR. OBTAINING DIFFERENT GRADATIONS IN DEVELOPINGv SILVER HALIDE EMULSION LAYERS Richard Schmidt, Dessau in Anhalt, Germany,

assignor to Agl'a Ansco Corporation, Binghamton, N. Y., a corporation of New York No Drawing. Application September 9, 1931., Sgrial No. 561,992. In Germany December 31, 1 28 e 4 Claims. (01. 95-88) My present invention relates to a process for obtaining different gradations when simultaneously developing silver halide emulsion layers exposed to light, these layers being on separate supports.

One of its objects is the process for obtaining such different gradations. Further objects will be seen from the detailed specification following hereafter.

I have found that an exposed silver halide emulsion layer is developed to a steeper gradation under the same conditions of developing if pretreated in a suitable bath, for instance, an alkali solution. Moreover, I have found that the degree of steepness of the said layer can easily be controlled by the concentration of the pretreating bath and the duration of its action. The higher the concentration of the bath and the longer it is allowed to act on the emulsion layer, the steeper is the gradation under the same conditions of developing.

As a pretreating bath any solution may be employed which together with the developing solution used in each particular case renders the gradation steeper. To this end the solution of alkalies, for instance, alkali carbonates or caustic alkalies are well suited; I prefer the carbonates. Instead of the alkalies other agents have proved useful for the purpose set forth, for instance, hardening agents, such as formaldehyde. The concentration of the bath may vary within wide limits, but a solution of about 2% strength gives the best results. The material to be treated may be immersed for about 1 to 3 minutes in the bath, which time was found to give good efiects. The action of the bath on the material may be shortened if desired, but a curve which, if possible, is free from sag. The developing solution is selected and standardized The negain such a manner that the sound film negative is developed without having subjected the filmto a pretreatment, so as to give a comparatively faint image. A developer of this kind is a solution of 4-methylaminophenol containing sodium sulfite. The most favorable concentration in each special case can easily be determined by a few experiments. The blackenings of the pretreated film negative appear immediately after pretreatment. Since this pretreating bath effects at the same time a certain reduction of the sensitiveness, it is especially suitedlin the development of pictures which have been exposed rather a long time.

My present invention is not limited to the foregoing examples nor to the specific details given therein. All developers known in the art may be used, preferably those poor in alkali. The

best working conditions of the pretreating bath with respect to concentration and duration of its action on the difierent emulsions may easily be determined by a few experiments. What I claim is:

1. A process of developing exposed silver halide emulsion layers being on separate supports to different gradations which comprises treating the layer to be developed to a steeper gradation, prior to development, with an alkali and then developing said layers simultaneously.

2-. A process of developing exposed silver halide emulsion layers being on separate supports to different gradations which comprises treating the layer to be developed to a steeper gradation, prior to development, with a solution containing an alkali carbonate and then developing said layers simultaneously. I

and sound film negative being on separate supports which comprises treating for 1 to 3 minutes the exposed picture'negative film, prior to development, with an aqueous solution of sodium carbonate of about 0.5 to 1 per cent strength and then developing said layers simultaneously.

RICHARD SCHMIDT. 

